1. Field of the Invention
The present invention is directed to a method and apparatus for detecting defective containers on a conveyor. More particularly, the invention relates to a method and apparatus for detecting bulges in crimped seams of metal cans.
2. Description of the Background Art
Metal cans and particularly aluminum cans are commonly used in the beverage industry. The use of aluminum cans is advantageous since the manufacture of cans is less expensive than other containers, and the cans are easily handled by automated equipment.
A disadvantage of using cans for beverages is the tendency of the seams between the lid and the sidewall to form improperly. Various defects in the seam can be very difficult to detect during the manufacturing and packaging operations. Moreover, slight defects in the seam can result in leakage of the contents long after the cans are shipped to the customer. Such latent leaks in the cans often result in significant losses and additional expenses for the manufacturer, since the manufacturer is typically responsible for replacing defective merchandise.
Several devices have been used to maintain quality control in the manufacture and filling of beverage cans. An example of one such device projects a low-intensity, gamma-radiation beam through the sidewall of the can to ensure that the can is filled to the proper level. A sensor is positioned on the opposite side of the can to measure the intensity of the beam passing through the can. Under normal conditions, the beam passes through the sidewall and through the contents of the can to provide a certain intensity detected by the sensor. When the contents are below the level of the beam, the sensor detects a different beam intensity which indicates an improperly filled can. Although an improperly filled can often is indicative of a defective seam, cans with latent leaks are not detectable.
Accordingly, there is a continuing need in the industry for a device that is capable of detecting defective seams in a continuous manufacturing assembly.